1. Field of the Invention
The present invention relates to a polarizing plate protective film, a dope composition, a method for manufacturing a polarizing plate protective film, a polarizing plate, and a liquid crystal display device.
2. Description of the Related Art
A demand for using a liquid crystal display device as a liquid crystal display or the like of a liquid crystal television or a personal computer has increased. In general, a liquid crystal display device is configured of a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, and the like are interposed between glass plates, and two polarizing plates disposed on both sides thereof, and each of the polarizing plates has a configuration in which a polarizer (also referred to as a polarizing film) is interposed between two optical films (polarizing plate protective films). In general, a cellulose triacetate film is used as the polarizing plate protective film.
On the other hand, the size of the liquid crystal display device has been rapidly enlarged, and the application of the liquid crystal display device has been diversified according to advancements in the recent technology. For example, the liquid crystal display device is used as a large display which is disposed on the street or in front of a store, a display for advertisement in a public place using a display device which is referred to as digital signage, and the like.
In such application, the liquid crystal display device is assumed to be used outside, and thus, deterioration due to moisture absorption of the polarizing film becomes a problem, and the polarizing plate protective film has been required to have higher moisture resistance. However, in a cellulose ester film such as a cellulose triacetate film which has been used in the related art, it is difficult to obtain sufficient moisture resistance, and recently, a device has been required to be thin, and thus, in a case where the film becomes thick in order to obtain moisture resistance, the polarizing plate itself also becomes thick.
On the other hand, polymethyl methacrylate (hereinafter, referred to as PMMA) which is a representative of an acrylic resin exhibits excellent transparency or excellent dimensional stability in addition to low hygroscopicity, and thus, has been preferably used as an optical film material having low hygroscopicity in the optical film.
For example, in JP2007-118266A, it is disclosed that an acrylic resin having a molecular weight of 80,000 to 150,000 is preferably used as the material of a polarizing plate protective film, and in JP2007-118266A, it is also disclosed that an acrylic resin film is formed by a solution film formation method.